CRTs include an electron gun device and a phosphor structure both of which are held within an evacuated enclosure. Typically, the enclosure includes a front panel section having a panel inner surface which includes the phosphor structure. In addition, the front panel includes a peripheral flange having a flange inner surface located adjacent to the panel inner surface.
The phosphor structure is formed by depositing phosphor that is in fluid form onto the panel inner surface. Frequently, the fluidic properties of the phosphor cause spreading of phosphor past the panel inner surface to the adjacent flange inner surface. The presence of phosphor on the flange inner surface results in many undesirable effects such as tube arcing and others. Consequently, it is desirable that the excess phosphor be removed from the flange inner surface to avoid such undesirable effects.
In order to remove the excess phosphor, CRT assembly lines include water trimmer systems each having a nozzle arrangement for discharging a continuous stream of water onto the phosphor. In operation, a front panel in the assembly line is transported to a water trimmer station and positioned such that water from the nozzle arrangement is discharged onto the flange inner surface, thus removing substantially all of the excess phosphor. The panel is then transported away from the water trimmer station to enable placement of the next front panel in the assembly line in the water trimmer station. A stream of water is continually discharged from the nozzle in such systems, including during the time interval between movement of a front panel away from the water trimmer station and placement of the next front panel in the water trimmer station. This is a disadvantage since a substantial amount of water is not utilized and thus wasted during each workday, which undesirably increases production costs. In addition, this water usage unnecessarily depletes limited water resources and is generally harmful to the environment. Furthermore, these disadvantages are exacerbated in areas of the country which are drought prone, such as in southern California.
In order to reduce the amount of water that is used, a solenoid valve has been added to such trimmer systems to control water discharge from the nozzle. The solenoid valve may be actuated so that it is in one of two positions. In a first position, an internal passageway within the valve is fully open to allow maximum water discharge from the nozzle. In a second position, the internal passageway is fully closed to stop water discharge from the nozzle. Referring to FIG. 1, a water discharge curve 11 for a trimmer system having a solenoid valve is shown. In the closed position, the valve stops water discharge from the nozzle as indicated by the first 10 and second 12 sections on the curve 11. Alternatively, in the open position, the valve allows maximum water discharge from the nozzle as indicated by the third section 14 on the curve 11. As such, the valve functions as an on/off valve. The transition between no water discharge and maximum water discharge occurs relatively instantaneously, as indicated by the substantially vertical sections 16,18 of the curve 11.
In operation, the valve is initially in the closed position (i.e. the first section 10) wherein no water is discharged from the nozzle. A front panel in the assembly line is then placed in the water trimmer station. The valve is then actuated such that it is in the completely open position (i.e. third section 14) which causes a maximum discharge of water from the nozzle and enables the removal of excess phosphor. Upon removal of the excess phosphor, the valve is actuated in order to return it to the closed position (i.e. the second section 12) wherein the discharge of water from the nozzle is stopped, thus reducing water usage.
However, such systems have disadvantages. In particular, it has been found that the relatively instantaneous transition between no water discharge and maximum water discharge, as indicated by vertical sections 16,18, results in splashing of water onto both the flange and panel inner surfaces. This undesirably removes phosphor from the panel inner surface as well as the flange inner surface. The removal of phosphor from the panel inner surface results in an unacceptable front panel that does not meet quality standards. As such, the panel must be either repaired or discarded, which decreases production yields and increases costs. Consequently, there is a need in the art for a phosphor removal system which reduces water usage and which substantially reduces splashing.